You’ve probably heard all about the immune benefits of vitamin C – but today it’s time to move one letter down the alphabet. It turns out that vitamin D may actually be the more critical vitamin when it comes to fighting off colds. An important member of Dr. Oz’s anti-aging checklist, vitamin D plays a number of roles in our bodies, including:

* Promoting absorption of calcium and bone health

* Boosting immune function
* Reducing inflammation
* Healthy neuro-muscular function
* Protecting against some forms of cancer

For such an amazing nutrient, vitamin D doesn’t always get the attention it deserves, perhaps because very few foods in nature contain vitamin D. The best sources are salmon, tuna and mackerel (especially the flesh) and fish liver oils. Beef liver, cheese and egg yolks also contain small amounts. If these foods don’t sound very appealing to you, there is good news: you don’t have to eat vitamin D to make sure you’re getting your daily dose! Vitamin D is actually produced in your body when ultraviolet rays from sunlight strike your skin. The UV rays trigger synthesis of vitamin D, which then gets converted in your liver into its active form.

This means one of the best ways to get vitamin D is to spend about 10-15 minutes a day outside in the sun. Keep in mind that wearing sunscreen will prevent you from getting adequate vitamin D outdoors. In the summertime, an easy solution is skipping sunscreen on your legs for the first 15 minutes in the sun. Just make sure you apply in time to prevent any burns or damage.

If this sounds complicated (or it’s cloudy!), there’s an even easier way to get your vitamin D: many foods in the American diet are fortified with this essential nutrient. In fact, fortified foods provide the majority of vitamin D in our diets. Almost all of the US milk supply is fortified with 100 units per cup – that’s about 25% – 50% of the recommended daily dose! This means milk packs a double punch for bone strength. Milk contains a good amount of calcium and the additional vitamin D to ensure that your body absorbs all that calcium.

So exactly how much Vitamin D should you aim for each day? The answer varies depending on your age.

* For ages 0-50 (including pregnant and lactating women), 5 mcg or 200 international units is adequate
* For ages 50-70, 10 mcg or 400 international units is better
* For ages 71+, aim for at least 15 mcg (600 international units)

So if preventing colon, prostate and breast cancers, building strong bones, fighting off colds, and slowing aging sounds like a good deal to you – look for in all in one simple package: vitamin D.